The present invention relates to a printer for printing on recording paper, which comprises a platen and a printer head incorporated in a frame. More particularly, the present invention relates to a structure for incorporating a print head in a frame.
A general structure of a conventional printer is now described briefly in the following with reference to FIG. 2. As shown in FIG. 2A, a printer includes a platen 101 and a thermal head 102. The platen 101 is rotatably supported about an axis 101a along the width direction of recording paper (not shown). More specifically, a stepping motor 104 is connected with the axis 101a via a train of gears 103. The rotational motion of the stepping motor 104 is decelerated by the train of gears 103, and is transmitted rearwardly to the axis 101a, and the platen 101 is appropriately intermittently rotated for feeding paper in the direction shown by an arrow in the figure. The thermal head 102 comprises a circuit substrate 111 attached to a support body 112. A heater and a semiconductor device 114 for driving the heater are formed on the circuit substrate 111. A sealing resin 115 is provided over the semiconductor device 114 for protection. The thermal head 102 is disposed so as to face the platen 101 via recording paper. The thermal head 102 is swingably supported about an axis 105. During a printing operation, a heater of the thermal head 102 is pressed against the recording paper. With this state maintained, the heater is electrically energized to print a line of letters on the recording paper. After the printing of the line, the platen 101 is rotated in the direction shown by the arrow to feed the recording paper.
FIG. 2B shows a schematic cross-sectional structure of the printer shown in FIG. 2A. The thermal head 102 is disposed so as to face the platen 101 via a recording paper 106. When the thermal head 102 is swung counterclockwise about the axis 105 that is in parallel with but different from the axis 101a of the platen 101, the heater above the axis 105 is pressed against the platen 101. In order to provide the pressing force, a spring member 107 intervenes between the thermal head 102 and a frame 108 of the printer. On the contrary, when the thermal head 102 is swung clockwise against the urging force by the spring member 107, the heater of the thermal head 102 is retracted from the platen 101.
FIG. 3 is a schematic side cross-section of a specific structural example of the printer shown in FIG. 2. A frame 108 is substantially in the shape of a rectangular parallelepiped having top, bottom, left, and right faces. In the figure, the top face, the bottom face and the right face are represented as U, D, and R, respectively. It should be noted that the left face L is on the side opposite to the right face R. The platen 101 is rotatably, axially supported between the left and right faces L and R of the frame 108. The thermal head 102 is also axially supported between the left and right faces L and R of the frame 108, and openably swings with respect to the platen 101. Printing is carried out between the platen 101 and the thermal head 102 on recording paper (not shown) fed from the side of the bottom face D of the frame 108 and then the recording paper is discharged to the side of the top face U of the frame 108.
In the conventional structure shown in FIG. 3, a support shaft 105 penetrating both of the left and right faces L and R of the frame 108 supports both end portions 102a (only one of them is shown in the figure) of the thermal head 102. Therefore, to incorporate the thermal head 102 into the frame 108, it is required that the support shaft 105 is first inserted from the right face R or the left face L of the frame 108, and a component for regulating the movement of the support shaft 105 in the thrust direction is then mounted. Subsequently, the thermal head 102 is incorporated from, for example, the top face U, and both of the end portions 102a of the thermal head 102 are engaged with the support shaft 105. In this way, in the conventional printer, assembly and disassembly of the thermal head 102 is bi-directional or tri-directional. More specifically, in order to mount the support shaft 105 and to engage the thermal head 102 with the support shaft 105, the operation has to be carried out from the right face R and/or the left face L and from the top face U of the frame 108. Further, when the thermal head 102 is removed in order to replace a component, for example, the support shaft 105 is required to be pulled out of the frame 108 in the thrust direction. Therefore, if a train of gears for deceleration and the like are disposed nearby, all of them must be removed.
FIG. 4 illustrates a conventional printer with its assembly improved, which is disclosed in Japanese Utility Model Application Laid-open No. Hei 7-5745. A frame 201 of a printer body rotatably, axially supports a platen 202. A heat sink 204 is provided for a thermal head 203. A pressing component 205 presses the thermal head 203 held by the frame 201 to the side of the platen 202. Protrusions 206 and 206 are formed on the lower side of both longitudinal ends of the heat sink 204 of the thermal head 203. Bushes 207 and 207 are fitted onto the protrusions 206 and 206, respectively. The bushes 207 are D-shaped in section with one side of their outer periphery cut off, and are press fitted into the protrusions 206. Engagement holes 208 and 208, into which the bushes 207 and 207 are fitted, are formed on the lower side of both ends of the frame 201. The engagement holes 208 have insert grooves 208a on the lower side and holes 208b having a diameter permitting rotation of the D-shaped bushes 207 in section on the upper side. It should be noted that the width of the insert grooves 208a is made smaller than the diameter of the D-shaped portions of the bushes 207 so that the bushes 207 may slide into the insert grooves 208a when the thermal head 203 is mounted to the frame 201 and the bushes 207 may be prevented from falling down when the mounted thermal head 203 is slanted to the side of the platen 202. In order to make a print face of the thermal head 203 closely contact the outer periphery of the platen 202, the holes 208b are made slightly larger than the bushes 207, thereby permitting the bushes 207 to rattle to some extent and preventing over-restriction. The pressing component 205 has in its front a spring member 209 for pressing the thermal head 203 mounted to the frame 201. Stopper portions 210 are formed at both ends of the pressing component 25. Holes 213, each of which is fitted onto protrusions 212 for positioning the frame 201 in a holder 211 at its back, are formed. In this case, it is constructed that a head-up lever 214 releases the pressure of the thermal head 203 on the printing side, and the stopper portions 210 of the pressing component 205 are adapted to slide into receiving windows 215.
When the printer shown in FIG. 4 is assembled, the heat sink 204 of the thermal head 203 is inserted from the side of the bottom face of the frame 201. Furthermore, the bushes 207 and 207 are inserted into the insert grooves 208a and 208a of the respective engagement holes 208 and 208, and are slid upwardly. Under the state that the entire bushes 207 and 207 enter into the holes 208b and 208b, the thermal head 203 is slanted to the side of the platen 202. With this structure, the thermal head 203 is held by the frame 201 with the bushes 207 being prevented from falling down from the engagement holes 208. However, in this conventional printer, the thermal head 203 is incorporated into the frame from the side of the bottom face. Generally, in such a case that an automatic assembly is performed, the less the directions of incorporation of components are, the better it is. In addition, incorporation from the side of the top face is more preferable than that from the side of the bottom face. However, in the conventional printer shown in FIG. 4, the thermal head 203 has to be incorporated from the side of the bottom face, and thus, a process of reversing the frame 201 and the like have to be added, leading to a problem that the handling is complicated.